1. Field of the Invention
The present invention relates to street sweepers or the like and more particularly relates to an improved multiple flight debris elevating system for the sweeper.
2. Description of the Prior Art
Elevating systems which use an enldess conveyor with flights thereon for elevating debris collected by a rotary broom are well known in the art as evidenced by United States Pat. No. 3,363,274 which issued to Tamny on Jan. 16, 1968; and U.S. Pat. No. 3,584,326 which issued to Woodworth on June 15, 1971. This type of elevator also requires expensive elevator take-up mechanisms which require considerable expenditures of time to maintain the elevators properly tensioned.
Several United States patents disclose single rotary type dirt elevators for use on sweepers when the required lift is very low. The following patents are representative of this type of elevator:
Mortensen U.S. Pat. No. 3,649,982 dated Mar. 21, 1972; Scharmann et al 3,668,730 dated June 13, 1972; Mortensen U.S. Pat. No. 3,726,109 dated Apr. 10, 1973; Oberdank U.S. Pat. No. 3,805,310 dated Apr. 23, 1974; and Overton U.S. Pat. No. 4,200,953 dated May 6, 1980.
Prior art sweepers which use only vacuum to elevate debris to the hopper are well known in the art. These sweepers are required to pick up heavy articles, such as metal bars about 1" in diameter and 3" long. Since air is used to pick up these heavy articles, the debris from the pick up broom swath is diverted from the pick-up broom swath to a narrow swath adjacent a gutter broom so that a relatively small debris inlet opening will collect all swept debris and elevate it to the hopper. By providing a small inlet opening, the air velocity is fast enough to pick up heavy articles. Since only air is used to pick up both heavy and light debris, one disadvantage is that the elevating power requirement is excessively high. A separate engine of about 120 horsepower is required for driving the blower which provides about 13,000 cubic feet per minute of air at a pressure of about 5" of water. Another disadvantage of air elevators is that the air velocity is very high (about 100 ft/second) thereby presenting a substantial dust control problem. Dust and solids enter the hopper but because of the very high air velocity, the dust does not have time to separate from the air with the result that a substantial cloud of dust is discharged from the hopper into the atmosphere. Another problem is that the air inlet does not span the swath of the pick-up broom and accordingly much fine debris in the pick-up broom swath is not picked up but remains on the surface being cleaned.